The dotted curve in Fig. 1 shows the result of Eq. (1) for a width \(W\) =1.3 \(\mu \) m, close to the dimensions of the device. From the excellent agreement both in shape and magnitude, combined with the derived long mean free path, we conclude that the low-\(T\)  transport in our current-annealed, suspended devices is close to the ballistic limit. As an important consequence, the peak mobility appears to be limited by boundary scattering set by the device dimensions and not by impurity scattering and yet larger mobilities should be achievable. Sub-linear behavior of \(\sigma (n)\) , reminiscent of Fig. 1, was previously observed in unsuspended samples [1]}, [2]} and interpreted as a combined contribution of short-range and long-range scatterers. Given that the device dimension is comparable to the mean free path, such an interpretation based on the diffusive transport does not seem to be warranted for our samples.
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